Enhanced second-harmonic generation in monolayer MoS₂ on suspended metallic nanostructures by plasmonic resonances

Abstract

Monolayer transition metal dichalcogenides (TMDs) possess large second-order nonlinear responses due to the broken inversion symmetry, which can extend their intriguing applications in nonlinear nanophotonics and optoelectronics. However, the atomic thickness of monolayer TMDs severely decreases the interaction length with free light with respect to bulk materials, leading to rather low second-harmonic generation (SHG) conversion efficiency. Here, we demonstrate a hybrid structure consisting of a monolayer MoS2 on a suspended perforated silver film, on which the SHG signal emitted from the monolayer MoS2 is enhanced by more than three orders of magnitude at room temperature. The pronounced SHG enhancement is attributed to the distinct electric field amplification nearby the nanoholes, which is induced by the symmetric surface plasmon polaritons (SPPs) existing in the ultrathin suspended silver grating. Our results reported here may establish the substrate-free engineering of nonlinear optical effects via plasmonic nanostructures on demand.

Parametric Nonlinear Optics with Layered Materials and Related Heterostructures

“…SHG enhancement in TMDs has been obtained also in combination with plasmonic nanostructures and metasurfaces. [ 226–230 ] Here, the maximum enhancement is obtained when the plasmonic resonance matches the FF or the SH frequency. Shi et al., have shown a $$\approx 400$$‐fold enhancement of the SHG in a 1L $$\mathrm{WS}_2$$ incorporated onto a 2D silver nanogroove grating, [ 226 ] which was finely tuned to match the band nesting (C exciton) resonant energy.…”

Giant Nonlinear Response of Monolayer MoS2 Induced by Optimal Field‐Enhancement Gain Mode on the Surface of Hyperbolic Metamaterials

“…The largest SHG enhancement is as high as 22 145 times with a conversion efficiency up to 1.1 × 10 −6 W −1 , which greatly improves the study of nanostructure-induced SHG enhancement of monolayer MoS 2 . [27,28] The wavevector matching condition is shown in the right column. Normally, the wavevector inside PHMM (K PHMM ) is larger than that in the free space (K free ).…”

“…The largest SHG enhancement is as high as 22 145 times with a conversion efficiency up to 1.1 × 10 −6 W −1 , which greatly improves the study of nanostructure‐induced SHG enhancement of monolayer MoS 2 . [ 27,28 ]…”

Giant Enhancement and Directional Second Harmonic Emission from Monolayer WS2 on Silicon Substrate via Fabry-Pérot Micro-Cavity

“…Many previous reports have been introduced to enhance the SHG intensity from TMD monolayers, such as SiO 2 dielectric microspheres, plasmonic nanostructures, − waveguides, bound states in the continuum resonance, , etc. By coupling the WS 2 monolayer to a silicon substrate with metal nanostructures, such as 2D silver nanogroove grating or perforated silver film, SHG is increased by 2 to 3 orders of magnitude due to the strong electric field amplification in plasmonic nanostructures. , For the applications of TMD to on-chip frequency converters, there are urgent demands on both high conversion efficiency and directional emission. Higher efficiency helps reduce the energy consumption, and directional emission boosts the beam utilization in far-field application scenarios such as optical fiber communication, laser printing, smartphones, and ultracompact light detection and ranging (LiDAR).…”